In general, your baby shouldn’t drink water until he's about 6 months old. Until then, he gets all the hydration he needs from breast milk or formula, even in hot weather.
Giving a baby younger than 6 months old too much water can interfere with his body's ability to absorb the nutrients in breast milk or formula. It can also cause his tummy to feel full, which curbs his desire to feed. (While small sips of water probably won't hurt your baby, it's best to check with his doctor during those first six months.)
In rare cases, a baby who drinks too much water can develop a condition known as water intoxication, which can cause seizures and even a coma. Water intoxication happens when too much water dilutes the concentration of sodium in the body, upsetting the electrolyte balance and causing tissues to swell.
